In the United States, pediatric health care providers are not doing enough testing of children's blood lead levels in many states, according to a study published Thursday in the journal Pediatrics.

When 38 states and the District of Columbia reported cases of elevated blood lead levels to the US Centers for Disease Control and Prevention from 1999 to 2010, most reported fewer than half of the numbers that were expected, the new study says. (An elevated blood lead level is considered to be greater than or equal to 10 micrograms per deciliter.)

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"The highest numbers of cases (found) are actually occurring in the South, which I've never heard personally discussed as where the lead poisoning problems are," said Dr. Eric Roberts, lead author of the study and a scientist at the California Environmental Health Tracking Program at the Public Health Institute, a nonprofit research organization. "The rate of undercounting is the most severe in the Western states."

Children are at higher risk for lead poisoning and more susceptible to the toxic effects than adults, according to the American Academy of Pediatrics Committee on Environmental Health. The window of greatest vulnerability is in the embryonic, fetal and early postnatal periods.

Lead exposure can affect nearly every system in the body and can damage the brain and nervous system. It can slow growth and development and lead to learning and behavior problems including reduced IQ, attention-deficit hyperactivity disorder, and hearing and speech problems. Which is why the CDC says there is no safe blood lead level in children.

Testing: It's the law

The way states screen and test for elevated blood lead levels varies widely across the United States. Recently, though, with advances in both epidemiology and statistics, official estimates of the prevalence of elevated blood lead levels have become available for each of the 50 states and the District of Columbia.

For the new study, Roberts and his co-authors compared each state's expected estimates for elevated blood lead levels with the actual numbers reported to the CDC's Childhood Lead Poisoning Prevention Program for children between the ages of 1 and 5 for the years 1999 through 2010.

The team generated the estimates by applying new statistical methods to the National Health and Nutrition Examination Survey, which assesses the health and nutritional status of adults and children in the US. Last year, Roberts and a colleague published their methodology for this in the journal Statistics in Medicine.

Roberts aimed to quantify the adequacy of state efforts with regard to lead testing.

"It's actually the law that all kids who qualify for Medicaid get tested for lead," he said. "So that's been an easy way for people to notice that the numbers don't add up and the majority of kids who qualify for Medicaid actually don't get tested."

Guidelines set forth by the American Academy of Pediatrics also encourage pediatric health care providers to rely on state- and local-level screening to determine who should be tested, but these recommendations are often difficult to access or defer to a provider's discretion.

When people in medicine or public health talk about lead poisoning, they tend to see it as a problem in the Midwest and Northeast.

"It's very easy to jump in with that," Roberts said. "So a pediatrician in California really -- without being laughed at -- could just sort of say that 'I don't think there's a problem here; the problem is in the Midwest and Northeast.' "

So, many health providers across the nation may not think there's a problem in their own communities. And they put their time and energy into taking care of other health needs rather than worrying about testing for lead.

"I was worried there might be places in the US that are not catching all the kids that they're supposed to, but I didn't really know," Roberts said. "But I can also imagine physicians doing an extremely good job. It really was a completely open question."

A lack of awareness

About 1.2 million children are estimated to have had elevated blood lead levels between 1999 and 2010. Yet only 606,709 cases were reported to the CDC in that time period, Roberts and his colleagues found.

"There are 12 states that didn't participate in CDC reporting," he said, explaining that every state probably keeps track of testing results in some way, with doctors forwarding numbers to state departments of health, but that information may not make it out to the CDC. Reporting is not required by every state, depending on individual state budgets and funding for lead programs.

Of the 38 reporting states, the majority (23 states) reported fewer than half of the expected number of elevated lead cases, and 11 states reported less than 20%.

Among the 615,704 children who were estimated to have had elevated blood lead levels that went unreported, more than half had not been reported because they had not been tested.

The highest numbers of children detected as having elevated blood lead levels reside in Northeastern and Midwestern states, the new study found, with far fewer cases identified in the South and West.

These results did not surprise Roberts: "If you believe there are a lot of kids with lead poisoning, then you test a lot, and you find them. But If you don't believe they're out there, then you don't test at all, and by golly, you're right, nobody tested positive."

"It's an extremely circular argument," he said.

"One of the most documented risk factors for having lead exposure is a kid living in a house that was built before the 1978 ban on lead paint," Roberts said. "And we tell ourselves, 'well, California is new. It doesn't have old structures.' "

California has a higher rate of 1- to 5-year-olds living in pre-1978 buildings than the national average, Roberts found.

"So it's not that folks are wrong to worry about old houses, dilapidated buildings, water infrastructure. That's all really valid," he said. However, he has "genuine concerns" that health care providers are testing based on assumptions rather than reality.

Lead poisoning can be prevented

Katrina Smith Korfmacher, associate professor in the Department of Environmental Medicine at the University of Rochester Medical Center, agreed that the historical focus of public health discussions of lead poisoning has been on the Northeast "due to the high concentrations of older housing in poor condition."

"Although this study may focus attention on the potentially unidentified children at risk in other areas, the need to reduce lead hazards in areas with large amounts of older housing remains critical," said Korfmacher, who was not involved in the new research.

Parents should be aware of potential lead sources in their children's environment including older housing, unsafe renovation practices, contaminated soil, lead in water pipes, "take-home" lead from parents' jobs and imported products. But, "they should ask their pediatrician to test 1- and 2-year-old children, as well as younger and older children who might be exposed to a source of lead," Korfmacher said.

"Most importantly, lead poisoning can be prevented but not effectively treated, so it is critical to identify and eliminate sources of lead in children's environments before they are poisoned," she said.

Budget cuts to the CDC's lead poisoning prevention programs have harmed states' ability to promote prevention, testing and followup for lead, she noted. Meanwhile, the new study cites an estimated $50 billion annual loss in economic productivity due to lead poisoning.

"Expanded funding for policies, programs and grants that prevent children's exposure to lead is critical," Korfmacher said. She added that, "preventing lead exposure is essential to reduce the enormous impact of lead on children's ability to learn, develop and become productive members of society."

On the rise once again

Lead poisoning was common among the ancient Romans, even though knowledge of its toxicity dates as far back as 2000 B.C., according to the World Health Organization. It's a problem humans still struggle with today.

The percentage of children in the US between the ages of 1 and 5 with elevated blood lead levels declined from 77.8% in the late 1970s to 4.4% in the early 1990s, according to the CDC. While phasing out leaded gasoline between 1976 and 1995, the US experienced an associated reduction of more than 90% in mean blood lead concentration.

Similar effects were recorded in Western Europe, Australia, Canada, New Zealand and South Africa, according to a 2010 WHO report, which notes a steady rise in global lead consumption between 1965 and 1990. Worldwide, blood lead levels began to decline in the 1990s with efforts to remove lead from well-known sources.

Some rapidly industrializing countries -- including China, El Salvador, India, Mexico and Thailand -- also saw declines in blood lead levels after the removal of lead from gasoline, according to the WHO. Unleaded gas accounts for an estimated 99% of total sales worldwide as of late 2010.

Exposure to lead and prevalence of poisoning vary greatly from country to country as well as from place to place within countries, according to the WHO. Smelting, mining and metal recycling operations remain significant problems.

Lead in gasoline has been the largest contributor to environmental lead contamination, but other sources of lead exposure are significant. These include active industry (such as mining), paints and pigments, solder in food cans, ceramic glazes, drinking water systems, the food chain (via contaminated soil), certain products including cosmetics and toys, and electronic waste (e-waste).

The largest current use of lead is in batteries for cars and other vehicles, which has caused a reversal in global consumption of lead. Today, consumption is increasing due to a demand for energy-efficient vehicles.

The amount of lead in our bodies now is 500 to 1,000 times greater than in those of our preindustrial counterparts, according to the WHO.